Liquid crystalline compositions

ABSTRACT

Liquid crystalline compositions having a cholesteric mesophase are disclosed. The compositions have extended mesomorphic ranges and are stable at relatively low temperatures. Uses of the novel compositions in various electro-optic applications are also disclosed.

United States atent [1 1 Haas et al.

[ Dec. 18, 1973 1 LIQUID CRYSTALLINE COMPOSITIONS [75] Inventors: WernerE. L. Haas; John B.

Flannery, Jr., both of Webster; Bela Mechlowitz, Rochester; James E.Adams, Ontario, all of NY.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: Sept. 13, 1971 [21] Appl. No: 180,019

[52] US. Cl 96/1 E, 252/408, 350/160 LC OTHER PUBLICATIONS LiquidCrystals Draw lntense Interest, C & EN, Nov. 1, 1971, pp. 20-23.

Kelker et 211., A Liquid-Crystalline (Nematic) Phase with a ParticularlyLow solidification Point, Angew, Chem. Internat. Edit, Vol. 8, No. 11,pp. 884-885, 1969).

V. A. UsolTseva et 111., Chemical Characteristics, Structure andProperties of Liquid Crystal Russian Chemical Reviews, Vol. 32, N0. 9,Sept, 1963, pp. 495-507.

Primary ExaminerGeorge F. Lesmes Assistant Examiner-M. B. WittenbergAzt0rney.1ames J. Ralabate et a1.

[57] ABSTRACT Liquid crystalline compositions having a cholestericmesophase are disclosed. The compositions have extended mesomorphicranges and are stable at relatively low temperatures. Uses of the novelcompositions in various electro-optic applications are also disclosed.

10 Claims, 10 Drawing Figures LIQUID CRYSTALLlNlE COMPOSITIONSBACKGROUND OF THE INVENTION This application relates to liquidcrystalline compositions and more particularly to optically negativeliquid crystalline compositions which have extended mesomorphictemperature ranges and which are stable at relatively low temperatures.

Liquid crystalline substances exhibit physical characteristics some ofwhich are typically associated with liquids and others which aretypically unique to solid crys tals. The name liquid crystals has becomegeneric to substances exhibiting these dual properties. Liquidcrystalsare known to appear in three different forms: the smectic,nematic and cholesteric forms. These structural forms are sometimesreferred to as mesophases thereby indicating that they are states ofmatter intermediate between the liquid and crystalline states. The threemesophase forms of liquid crystals mentioned above are characterized bydifferent physical structures wherein the molecules of the compound arearranged in a manner which is unique to each of the three mesomorphicstructures. Each of these three structures is well known in the liquidcrystal art.

Some liquid crystalline substances possess optically negativecharacteristics. Birefringence, also referred to as double refraction,is an optical phenomenon characteristic of some solid crystals and mostliquid crystal substances. When a beam of unpolarized light strikes abirefringent substance it is split into two polarized components whosetransverse vibrations are at right angles to each other. The twocomponents are transmitted at different velocities through the substanceand emerge as beams of polarized light. By the term optically negativeliquid crystalline substances, as used herein, is meant those for whichthe extra-ordinary index of refraction 1 is smaller than the ordinaryindex of refrac tion 1 Cholesteric liquid crystal substances exhibitthis property. For a detailed description of this phenomenon see OpticalCrystallography, Wahlstrom, fourth Edition, Wiley and Sons, 1nc., NewYork.

The molecules in cholesteric liquid crystals are arranged in very thinlayers with the long axes of the molecules parallel to each other and tothe plane of the layers within each layer. Because of the asymmetry andsteric nature of the molecules the direction of the long axes of themolecules in each layer is displaced slightly from the correspondingdirection in adjacent layers. This displacement is cumulative oversuccessive layers so that overall displacement traces out a helicalpath. A comprehensive description of the structure of cho' lestericliquid crystals is given in Molecular Structure and the Properties ofLiquid Crystals," G. W. Gray, Academic Press 1962.

Cholesteric liquid crystals have the property that when the propagationdirection of plane polarized or unpolarized light is along the helicalaxis thereof, i.e., when the light enters in a direction perpendicularto the long axes of the molecules, (neglecting absorptionconsiderations), this light is essentially unaffected in transmissionthrough thin films of such liquid crystals except for a wavelength bandcentered about some wavelength A where A, 2np with n representing theindex of refraction of the liquid crystal substance and p the pitch orrepetition distance of the helical structure. The bandwidth AA of thiswavelength band centered about A, will typically be of the order ofabout (A, /14). For

light of a wavelength A the cholesteric liquid crystal, under theseconditions, exhibits selective reflection of the light such thatapproximately 50 percent of the light is reflected and approximately 50percent is transmitted, assuming negligible absorption which is usuallythe case, with both the reflected and transmitted beams beingapproximately circularly polarized in opposite directions.

For light having wavelengths around A but not at A the same effect ispresent but not as pronounced. The transmitted light is not circularlypolarized but is instead elliptically polarized. The chlolesteric liquidcrystals which exhibit this property of selective reflection of light ina region centered around some wavelength A,, are said to be in theGrandjean or disturbed" texture. If A, is in the visible spectrum theliquid crystalline film appears to have the color corresponding to A,and if A,, is outside the visible spectrum the film appears colorless.

Depending upon the intrinsic rotary sense of the helix, i.e., whether itis right-handed or left-handed, the light that is transmitted in theregion about A, is either right-hand circularly polarized light (RHCPL)or lefthand circularly polarized light (LHCPL). The transmitted light iscircularly polarized with the same sense of polarization as thatintrinsic to the helix. Thus, a cholesteric liquid crystal having anintrinsic helical structure which is left-handed in sense will transmitLHCPL and one having a helical structure which is righthanded in sensewill transmit Rl-lCPL.

Hereinafter these cholesteric liquid crystal substances will beidentified in order to conform with popular convention, by the kind oflight which is reflected at A When a film is said to be right-handed, itis meant that it reflects RHCPL, and when a film is said to beleft-handed, it is meant that it reflects LHCPL.

A right-handed cholesteric liquid crystal substance transmits LHCPLessentially completely at A whereas the same substance reflects almostcompletely RHCPL. Conversely a left-handed film is almost transparent toRHCPL at A and reflects LHCPL. Since plane polarized or unpolarizedlight contain equal amounts of RHCPL and LHCPL, a cholesteric liquidcrystal film is approximately 50 percent transmitting at A, for thesesources when the liquid crystal is in its Grandjean texture.

A further unique optical property of optically negative liquid crystalfilms is that contrary to the normal situation when light is reflected,such as by a mirror, where the sense of the circular polarization of thereflected light is reversed, this same phenomenon does not occur withlight reflected by these liquid crystal films. The sense of the circularpolarization of light reflected from these liquid crystal substances isnot reversed but rather remains the same as it was before it came intocontact with the liquid crystal substance. For example, if RHCPL havinga wavelength A, is directed at a right-hand film having A 2np it issubstantially completely reflected and, after reflection, remains RHCPL.If the same light were to be directed on a mirror the reflected lightwould be LHCPL.

Because of these optical properties optically negative liquidcrystalline substances have been found to be highly advantageous for usein a number of applications. Copending patent applications Ser. No.104,367 now U.S. Pat. No. 3,669,525 and Ser. No. 104,369 now U.S. Pat.No. 3,679,290, both filed Jan. 6, 1971 disclose the use of such liquidcrystalline materials in optical filter systems. Copending patentapplication Ser. No. 104,344, filed Jan. 6, 197], discloses the use ofthese materials in a detection system which can identify physicalsurface and/or electrical conductivity irregularities in a surface ofinterest.

One difficulty with respect to potential uses of chlesteric liquidcrystalline materials in electro-optic devices has been the relativelyhigh temperatures at which the majority of the known cholestericmaterials become mesomorphic. Typically, electro-optic devices areoperated at or near room temperature. Thus devices utilizing cholestericliquid crystalline materials having relatively high mesomorphictemperature ranges would require additional apparatus-to maintain thetemperature of the liquid crystalline materials within their mesomorphicrange thereby undesirably complicating the overall device configuration.Therefore there exists a continuing need for cholesteric liquidcrystalline materials which have mesomorphic temperature ranges at ornear room temperature.

SUMMARY OF THE INVENTION It is therefore an object of this invention toprovide liquid crystalline materials having the above-describeddesirable features.

It is another object of the invention to provide novel liquidcrystalline compositions.

It is a further object of the invention to provide liquid crystallinecompositions having cholesteric mesomorphic temperature ranges which aresignificantly larger than those of the individual components thereof.

It is a still further object of the invention to provide liquidcrystalline compositions which have a cholesteric mesophase at or nearroom temperature.

Yet another object of the invention is to provide such liquidcrystalline compositions which are useful in electro-opticalapplications.

A still further object of the invention is to provide such liquidcrystalline compositions which may be utilized in electro-optic imagingand display devices.

These and other objects and advantages of the invention are accomplishedby providing novel optically negative liquid crystalline compositionswhich are formed by mixing together cholesteric liquid crystallinematerials with particular combinations of liquid crystalline compoundshaving a general formula and which have a nematic mesophase which isstable at relatively low temperatures. Liquid crystalline compoundswhich belong to the class of compounds having the general formula andwherein R and R are particular combinations of alkyl groups aredisclosed in copending application Ser. No. 179,732 filed Sept. 13, 1971on the same day as the present application. The novel compoundsdisclosed in the copending application are listed in Table I.

TABLE I Smectic Nematlc It has also been found that by utilizing some ofthe compounds listed in Table I and other members of the same genericclass it is possible to form compositions which have significantlylarger nematic mesomorphic temperature ranges than those of theindividual compounds. These novel nematic liquid crystallinecompositions are disclosed in copending application Ser. NO. 179,731filed Sept. 13, 1971 on the same day as the present application. Thenovel liquid crystalline compositions described in the copendingapplication are: mixtures of p-methoxybenzylidene-p'-n-butylaniline(R,=CH and R =C H (hereinafter referred to as ABUTA for simplicity) andp-n-butoxybenzylidene-p'- n-butylaniline (hereafter EOBUTA); mixtures ofpethoxybenzylidene-p'-n-butylaniline (R =C H and R =C H (hereafterEOBUTA) and ABUTA; mixtures of EOBUTA and BOBUTA; mixtures ofp-nbutoxybenzylidene p'-ethylaniline (hereinafter BOE- THA) and ABUTA;mixtures of BOETHA and EOBUTA; mixtures ofp-n-pentyloxybenzylidene-p-nbutylaniline (hereinafter PENTOBUTA) andABUTA; and mixtures of p-n-hexyloxybenzylidene-p'-nbutylaniline(hereinafter HEXOBUTA) and ABUTA. These compositions typically havenematic mesomorphic temperature ranges which are stable at roomtemperature or slightly below and in some cases significantly below,typically extending to below 0C.

Now it has been surprisingly found that optically negative liquidcrystalline compositions which have a cholesteric mesophase at, near orbelow room temperature can be formed by mixing together a suitablecholesteric liquid crystalline substance, or mixture of thesesubstances, with the compositions listed above. In other words, each ofthe nematogenic compositions previously described can be mixed togetherwith a sufficient amount of any suitable cholesteric liquid crystallinematerial, or combination thereof, to form liquid crystallinecompositions which have optically negative characteristics. Theoptically negative compositions of the invention have a cholestericmesomorphic temperature range which is significantly larger than thoseof the individual components thereof.

The invention will be more readily understood from the followingdetailed description of preferred embodiments thereof particularly whenread in conjunction with the accompanying drawings wherein:

FIGS. ll-7 are graphical plots illustrating the eutectic behavior of therespective nematogenic compositions to form the optically negativecompositions of the invention;

FIG. 8 graphically illustrates the liquid crystalline mesomorphictemperature characteristics of typical optically negative compositionsof the invention;

FIG. 9 graphically illustrates the liquid crystalline mesomorphictemperature characteristics of other typical optically negativecompositions of the invention;

FIG. 10 is a partially schematic cross-sectional view of a liquidcrystalline imaging member.

Generally speaking, the individual nematogenic compounds employed in theoptically negative liquid crystalline compositions of the invention areprepared by condensation in refluxing ethanol of the respectivep-nalkoxybenzaldehyde and the appropriate p-nalkylaniline. Refluxing iscarried out for several hours and the solvent is then removed bydistillation. The crystalline products are then purified by repeatedcrystallization from an appropriate solvent such as methanol orpetroleum ether. For a detailed description of the procedures used informing these compounds see copending application Ser. No. 179,732,filed Sept. 13, 1971 on the same day as the present application.

The nematogenic compositions are prepared by weighing appropriatefractions of the desired constituents, combining them in a vessel, e.g.,a glass beaker, and heating above the isotropic transition temperaturesof the respective constituents with mixing to ensure a homogeneouscomposition. FIGS. l-7 illustrate the eutectic behavior of therespective nematogenic compositions utilized to form the opticallynegative compositions of the invention. The temperatures at whichtransitions from the nematic mesomorphic state to the isotropic stateoccur, as indicated in FIGS. 1-7 for the respective compositions, aredetermined by differential thermal analysis employing a duPont 900Differential Thermal Analyzer equipped with chrome] alumelthermocouples. The thermograms are obtained at a heating rate of10C/minute and the temperature at the beginning of the state transitionendotherm is taken as the characteristic temperature. The temperature isdetermined by linear extrapolation of the leading edge of the endothermto its intersection with the baseline. Verification of the stateassignments is obtained by polarized optical microscopy. Samples of thecompositions are placed, in the form of thin films, between glass coverslides and viewed through a Leitz Ortholux polarizing microscope havinga calibrated hot stage. Visually observed changes have been found tocoincide within 2C with the phase transitions observed by thermalanalysis.

The optically negative compositions of the invention are formed bymixing each of the nematogenic compositions described above with anysuitable cholesteric liquid crystalline material or mixture ofcholesteric liquid crystalline materials. Of course it will beunderstood that the amount of the cholesteric component must besufficient to provide optically negative characteristics to the overallcompositions. Generally speaking the optically negative liquidcrystalline compositions of the invention comprise from about 5 percentto about 99 percent by weight of the cholesteric liquid crystallinecomponent and from about 1 percent to about 95 percent by weight of thenematogenic liquid crystalline composition. FIG. 8 illustrates thecholesteric mesomorphic liquid crystalline characteristics of a typicalcomposition of the invention. Referring now to FIG. 8 there is seen agraphical plot showing the cholesteric mesomorphic temperaturecharacteristics of compositions formed from varying weight percentagescholesteryl oleyl carbonate (a cholesteric liquid crystalline substance)and a 60/40 per cent by mixture of ABUTA and BOBUTA. Various mixtures ofthe two components are made and their isotropic transition temperatures,i.e. the temperature at which they become a true liquid, are determined.These isotropic transition temperatures are plotted in FIG. 8. All ofthe compositions are observed to have a cholesteric liquid crystallinemesophase at room temperature. Moreover at a concentration of percent byweight of the cholesteryl oleyl carbonate, the composition is observedto have a smectic to cholesteric phase transition temperature of about1C. Since cholesteryl oleyl carbonate has a cholesteric mesomorphictemperature range of from about 20C to about 29C, then by interpolationthe dotted line A, can be drawn to give an approximation of thecholesteric phase temperature ranges for the system shown.

FIG. 9 illustrates another typical composition of the invention.Referring now to FIG. 9 there is seen a graphical plot showing thecholesteric mesomorphic temperature characteristics of compositionsformed from varying weight percentages of cholesteryl oleyl carbonateand a /40 percent by weight mixture of ABUTA and EOBUTA. Again, asabove, various mixtures of the two components are made and theirisotropic transition temperatures determined. The isotropic transitiontemperatures are plotted in FIG. 9. All of the compositions are observedto have a cholesteric liquid crystalline mesophase at room temperature.At a composition of 50 percent by weight of cholesteryl oleyl carbonatethe composition is observed to have a smectic to cholesteric phasetransition temperature of about 5C. Again using the lower limit of thecholesteric mesomorphic temperature range it is possible to interpolateto obtain an approximation of the cholesteric phase temperature rangesfor the system shown. Dotted line B indicates the approximate lowerlimit of the cholesteric temperature range for the system.

Of course it will be understood that the systems shown in FIGS. 8 and 9are intended to be exemplary since, as was stated previously, anysuitable cholesteric liquid crystalline material may be combined withthe nematic mixtures specified and typically form optically negativecompositions having extended mesomorphic temperature ranges. Typicalsuitable cholesteric liquid crystalline materials include, for example,derivatives from reactions of cholesterol and inorganic acids, forexample, cholesteryl chloride, cholesteryl bromide, cholesteryl iodide,cholesteryl nitrate; esters derived from reactions of cholesterol andcarboxylic acids; for example cholesteryl crotonate; cholesterylnonanoate; cholesteryl hexanoate; cholesteryl formate; cholesteryldocosonoate; cholesteryl chloroformate; cholesteryl propionate;cholesteryl acetate; cholesteryl valerate; cholesteryl vacconate;cholesteryl linolate; cholesteryl linolenate; cholesteryl oleate;cholesteryl erucate; cholesteryl butyrate; cholesteryl caprate;cholesteryl laurate; cholesteryl myristate; cholesteryl clupanodonate;ethers of cholesterol such as cholesteryl decyl ether; cholesteryllauryl ether; cholesteryl oleyl ether; cholesteryl dodecyl ether;cholesteryl oleyl ether; cholesteryl dodecyl ether; carbamates andcarbonates of cholesterol such as cholesteryl decyl carbonate;cholesteryl oleyl carbonate; cholesteryl methyl carbonate; cholesterylethyl carbonate; cholesteryl butyl carbonate; cholesteryl docosonylcarbonate; cholesteryl cetyl carbonate; cholesterylheptyl carbamate; andalkyl amides and aliphatic secondary amines derived from 3 fi-amino- A-cholestene and mixtures thereof; peptides such aspolyy-benzyll-glutamate; derivatives of beta sitosterol such assitosteryl chloride; and active amyl ester of cyano benzylidene aminocinnamate. The alkyl groups in said compounds are typically saturated orunsaturated fatty acids, or alcohols, having less than about 25 carbonatoms, and unsaturated chains of less than about five double-bondedolefinic groups. Aryl groups in the above compounds typically comprisesimply substituted benzene ring compounds. Any of the above compoundsand mixtures thereof may be suitable for cholesteric liquid crystallinecompositions in the present invention. The novel cholesteric liquidcrystalline compositions of the present invention may be advantageouslyemployed in various electro-optic applications such as imaging anddisplay devices. Copending patent application Ser. No. 821,565, filedMay 5, 1969 now U.S. Pat. No. 3,652,148 and hereby incorporated hereinby reference discloses a system wherein an optically negative liquidcrystalline substance is transformed to an optically positive liquidcrystalline mesophase by an applied electric field. Copending patentapplication Ser. No. 867,593, filed Oct. 20, 1969 now U.S. Pat. No.3,642,348 and hereby incorporated by reference herein discloses a systemwhich transforms a cholesteric liquid crystalline material from itsGrandjean or disturbed texture state to its focalconic or undisturbedtexture state by an applied electric field.

In FIG. a typical liquid crystalline imaging member 10, sometimesreferred to as an electroded imaging sandwich, is shown in partiallyschematic cross-section where a pair of transparent plates 11 havingsubstantially transparent conductive coating 12 upon the contactsurface, comprise a parallel pair of substantially transparentelectrodes. An imaging member wherein both electrodes are transparent ispreferred where the imaging member is to be viewed using transmittedlight; however, a liquid crystalline imaging member may also be viewedusing reflected light thereby requiring only a single transparentelectrode while the other may be opaque. The transparent electrodes areseparated by spacing member 13 which contains voids which form one ormore shallow cups which contain the liquid crystalline film or layerwhich comprises the active element of the imaging member. A field iscreated between the electrodes by an external circuit 15 which typicallycomprises a source of potential 16 which is connected across the twoelectrodes through leads 17. The circuit 15 may also contain suitableswitching means. The potential source may be either D.C., A.C., or acombination thereof.

According to the system described in copending application Ser. No.867,593, when cholesteric liquid crystals or a mixture of cholestericliquid crystalline substances is used in an electrode sandwich such asdescribed in FIG. 10, electric fields applied across the liquidcrystalline film cause an electrical field-induced texture transition tooccur wherein a cholesteric liquid crystalline material initially in itsGrandjean or disturbed texture is transformed to its focal-conic orundisturbed texture. The Grandjean texture is typically characterized byselective dispersion of incident light around a wavelength A, (where A2np where n the index of refraction of the liquid crystalline film and pthe pitch of the liquid crystalline film) and optical activity forwavelengths of incident light away from A If h is in the visiblespectrum, the liquid crystalline film appears to have the colorcorresponding to )t and if A, is outside the visible spectrum the filmappears colorless and non-scattering. The Grandjean texture ofcholesteric liquid crystals is sometimes referred to as the disturbedtexture.

The focal-conic texture is also typically characterized by selectivedispersion but in addition this texture also exhibits diffuse scatteringin the visible spectrum, whether A is in the visible spectrum or not.The appearance of the focal-conic texture state is typically milky-whitewhen A is outside the visible spectrum. The focal-conic texture ofcholesteric liquid crystals is sometimes referred to as the undisturbedtexture.

For example, in this system when cholesteric liquid crystals are placedin the unbiased electrode sandwich, they initially appear colored, orcolorless and transparent. If the electrode sandwich is observed betweenpolarizers the imaging sandwich appears colored or black. When theelectrical field is placed across the liquid crystalline film, thefield-induced texture change is observable because the liquidcrystalline film becomes white in the imaged area when the imagingsandwich is observed in transmitted or reflected light. The describedimaging system thereby produces a white image on a dark or coloredbackground. However, it is clear that either field or non-field areas inthe liquid crystalline imaging sandwich may be used to create thedesired image, with or without the use of polarizers or other imageenhancing devices.

The system described in copending application Ser. No. 821,565, filedMay 5, 1969 now U.S. Pat. No. 3,652,148 is similar to that justdescribed but typically uses higher voltages and field strengths,(relative to those used in the system of application 827,593) totransform an optically negative liquid crystalline substance to anoptically positive liquid crystalline meso phase. However the respectiveprocesses produce entirely different effects as will be appreciated bythose skilled in the art.

In the liquid crystal imaging member described in FIG. 10 the electrodesmay be of any suitable transparent conductive material. Typical suitabletransparent, conductive electrodes include glass or plastic substrateshaving substantially transparent and continuously conductive coatings ofconductors such as tin, indium oxide, aluminum, chromium, tin oxide, orany other suitable conductor. These substantially transparent conductivecoatings are typically evaporated onto the more insulating, transparentsubstrate. NESA glass, a tin oxide coated glass manufactured by thePittsburgh Plate Glass Co., is a commercially available example of atypical transparent, conductive electrode material.

The spacer, 13 in FIG. 11.0, which separates the transparent electrodesand contains the liquid crystal film between said electrodes, istypically chemically inert, transparent, substantially insulating andhas appropriate dielectric characteristics. Materials suitable for useas insulating spacers include cellulose acetate, cellulose triacetate,cellulose acetate butyrate, polyurethane elastomers, polyethylene,polyproylene, polyesters, polystyrene, polycarbonates,polyvinylfluoride, polytetrat'luoroethylene, polyethylene terephthalate,and mixtures thereof.

Such spacers, which also approximately define the thickness of theimaging layer or film of liquid crystals, are preferably of a thicknessin the range of about 10 mils or less. Optimum results are typicallyattained with spacers in the thickness range between about Mr mil andabout mils.

It will be further recognized that the devices used in the imagingsystems just described may be modified. For example, at least one of theelectrodes shown in FIG. may be provided in image configuration therebyproviding a system where the desired image is defined by the shape ofone of the electrodes, or the desired image may be defined by the shapeof the spacing member; or at least one of the electrodes may also be aphotoconductor and an imagewise field may be applied across thecholesteric liquid crystalline film by means of an imagewise pattern ofactivating radiation being directed upon the imaging cell while apotential is applied to the electrodes.

The novel cholesteric liquid crystalline compositions of the inventionwill now be further described with respect to specific preferredembodiments by way of Examples it being understood that these areintended to be illustrative only and the invention is not limited to thematerials, proportions, etc. recited therein. All parts and percentageslisted are by weight unless otherwise specified.

EXAMPLES All of the compositions listed in the following Examples areprepared by placing the contituents in a vessel, heating above theisotropic transition temperatures of the constituents with mixing toensure a homogeneous composition. The isotropic transition temperaturesare determined by differential thermal analysis.

EXAMPLE I A cholesteric liquid crystalline composition is prepared from10 percent cholesteryl erucate, 54 percent ABUTA and 36 percent BOBUTA.The composition is cholesteric at room temperature and has an isotropictransition temperature of about 44C.

EXAMPLE II A cholesteric liquid crystalline composition is prepared frompercent cholesteryl erucate, 48 percent ABUTA and 32 percent BOBUTA. Thecomposition is cholesteric at room temperature and has an isotropictransition temperature of about 44C.

EXAMPLE III A cholesteric liquid crystalline composition is preparedfrom 90 percent cholesteryl erucate, 6 percent ABUTA and 4 percentBOBUTA. The composition has an isotropic transition temperature of about43C.

EXAMPLE IV A cholesteric liquid crystalline composition is prepared from10 percent cholesteryl erucate, 54 percent ABUTA and 36 percent EOBUTA.The composition is cholesteric at room temperature and has an isotropictransition temperature of about 46C.

EXAMPLE v EXAMPLE VI A cholesteric liquid crystalline composition isprepared from percent cholesteryl erucate, 6 percent ABUTA and 4 percentEOBUTA. The composition has an isotropic transition temperature of about42C.

EXAMPLES vrr a xx The compositions are formed with the listedpercentages of the individual constituents. All of the compositions arecholesteric at room temperature. The approximate transition temperaturesare shown Smectic Chol Transition 50 cholesteryl oleyl 4 carbonate 35%ABUTA 15% BOETHA 50% cholesteryl oleyl carbonate 40% EOBUTA l0% BOETHA50% cholesteryl oleyl 0 carbonate 30% ABUTA 20% PENTOBUTA 50%cholesteryl olcyl carbonate 30% ABUTA 20% HEXOBUTA 50% cholesteryl olcyll carbonate 30% ABUTA 20% BOBUTA XII 50% cholesteryl olcyl 5 carbonate30% ABUTA 20% EOBUTA 50% cholesteryl oleyl carbonate 30% EOBUTA 20%BOBUTA 20% cholesteryl erucate 3 64% EOBUTA l6% BOETHA 20% cholesterylcrucatc 48% ABUTA 32% PENTOBUTA cholesteryl erucate 48% ABUTA 32%HEXOBUTA 20% cholesteryl erucate 48% ABUTA 32% BOBUTA 20% cholesterylerucate 48% ABUTA 32% EOBUTA 20% cholesteryl erucate 2 48% EOBUTA 32%BOBUTA 20% cholesteryl erucatc 56% ABUTA 24% BOETHA Chol IsotropicTransition EXAMPLE VII VIII 50 XIIl 52 XIV 66 XVI 52 XVII 44 XVIII 46XIX 68 rial and from about l to about 95 weight percent of a nematicliquid crystalline composition comprising from about 55 to about 65weight percent of and from about 35 to about 45 weight percent of layerwhile said composition is in the cholesteric liquid crystalline phase tocause an imagewise change in the appearance of image portions of saidimaging material layer while the background portions of said materiallayer retain an appearance substantially distinguishable from the imageportions of said layer.

3. The process as defined in claim 2 wherein a pair of conductiveelectrode members are provided in spaced relationship, at least one ofsaid electrodes being at least partially transparent,

placing said imaging material layer between said members and applying anelectrical field between said members while said composition is in thecholesteric liquid crystalline phase to cause a change in the appearanceof said composition in an imagewise configuration.

4. The process as defined in claim 3 wherein at least one of saidelectrodes is shaped in image configuration.

5. The process as defined in claim 3 wherein at least one of saidelectrodes includes a photoconductive surface and said imagewiseelectrical field is applied across said imaging material layer byexposing said photoconductive surface to an imagewise pattern of activating radiation while applying a potential to said electrodes.

6. The method of producing a display comprising providing a displaydevice comprising first and second spaced plates, at least one of whichis substantially transparent, a plurality of parallel electricallyconductive films on one face of said first plate, a plurality ofparallel electrically conductive films on one face of said second plate,the plurality of films on at least one plate being substantiallytransparent, said two plates being positioned with faces bearing saidparallel conductive films adjacent and parallel to each other and thedirection of said conductive films on one plate being perpendicular tothe direction of said conductive films on the other plate, and a liquidcrystalline material comprising a composition of claim 1 filling thespace between said plates and selectively energizing at least oneconductive film on each plate while said composition is in thecholesteric liquid crystalline phase to cause an electric field to beselectively applied across said liquid crystalline material whereby animage is observed.

7. Liquid crystalline compositions having a cholesteric mesophasecomprising from about 5 to about 99 weight percent of a cholestericliquid crystalline material and from about I to about 95 weight percentof a nematic liquid crystalline composition comprising from about 50 toabout weight percent of and from about 30 to about 50 weight percent of8. Liquid crystalline compositions having a cholesteric mesophasecomprising from about 5 to about 99 weight percent of a cholestericliquid crystalline material and from about 1 to about 95 weight percentof a nematic liquid crystalline composition comprising from about 60 toabout weight percent of and from about 20 to about 40 weight percent of9. Liquid crystalline compositions having a cholesteric mesophasecomprising from about 5 to about 99 weight percent of a cholestericliquid crystalline material and from about 1 to about weight percent ofa nematic liquid crystalline composition comprising from about 50 toabout 80 weight percent of and from about 20 to about 50 weight percentof 10. Liquid crystalline compositions having a cholesteric mesophasecomprising from about 5 to about 99 weight percent of a cholestericliquid crystalline material and from about 1 to about 95 weight percentof a nematic liquid crystalline composition comprising from about 50 toabout 70 weight percent of and from about 30 to about 50 weight percentof

2. An imaging process comprising providing a layer of an imagingmaterial comprising a composition of claim 1 and providing an imagewiseelectrical field across said layer while said composition is in thecholesteric liquid crystalline phase to cause an imagewise change in theappearance of image portions of said imaging material layer while thebackground portions of said material layer retain an appearancesubstantially distinguishable from the image portions of said layer. 3.The process as defined in claim 2 wherein a pair of conductive electrodemembers are provided in spaced relationship, at least one of saidelectrodes being at least partially transparent, placing said imagingmaterial layer between said members and applying an elEctrical fieldbetween said members while said composition is in the cholesteric liquidcrystalline phase to cause a change in the appearance of saidcomposition in an imagewise configuration.
 4. The process as defined inclaim 3 wherein at least one of said electrodes is shaped in imageconfiguration.
 5. The process as defined in claim 3 wherein at least oneof said electrodes includes a photoconductive surface and said imagewiseelectrical field is applied across said imaging material layer byexposing said photoconductive surface to an imagewise pattern ofactivating radiation while applying a potential to said electrodes. 6.The method of producing a display comprising providing a display devicecomprising first and second spaced plates, at least one of which issubstantially transparent, a plurality of parallel electricallyconductive films on one face of said first plate, a plurality ofparallel electrically conductive films on one face of said second plate,the plurality of films on at least one plate being substantiallytransparent, said two plates being positioned with faces bearing saidparallel conductive films adjacent and parallel to each other and thedirection of said conductive films on one plate being perpendicular tothe direction of said conductive films on the other plate, and a liquidcrystalline material comprising a composition of claim 1 filling thespace between said plates and selectively energizing at least oneconductive film on each plate while said composition is in thecholesteric liquid crystalline phase to cause an electric field to beselectively applied across said liquid crystalline material whereby animage is observed.
 7. Liquid crystalline compositions having acholesteric mesophase comprising from about 5 to about 99 weight percentof a cholesteric liquid crystalline material and from about 1 to about95 weight percent of a nematic liquid crystalline composition comprisingfrom about 50 to about 70 weight percent of
 8. Liquid crystallinecompositions having a cholesteric mesophase comprising from about 5 toabout 99 weight percent of a cholesteric liquid crystalline material andfrom about 1 to about 95 weight percent of a nematic liquid crystallinecomposition comprising from about 60 to about 80 weight percent of 9.Liquid crystalline compositions having a cholesteric mesophasecomprising from about 5 to about 99 weight percent of a cholestericliquid crystalline material and from about 1 to about 95 weight percentof a nematic liquid crystalline composition comprising from about 50 toabout 80 weight percent of
 10. Liquid crystalline compositions having acholesteric mesophase comprising from about 5 to about 99 weight percentof a cholesteric liquid crystalline material and from about 1 to about95 weight percent of a nematic liquid crystalline composition comprisingfrom about 50 to about 70 weight percent of